Intracellular pH of barnacle and rat muscle fibers, and its regulation. Proton pumping and passive proton trans-membrane movements facilitated by weak acids and bases. Both intracellular pH-sensitive microelectrodes and DMO will be used. BIBLIOGRAPHIC REFERENCES: "Intracellular pH and Distribution of Weak Acids across Cell Membranes. A Study of D- and L-lactate and of DMO in Rat Diaphragm." by A. Roos J. Physiol. 249, 1, 1975.